Conventionally, as an electronic device of insertion mount structure, a connector terminal inserted in the through-hole of a circuit board (i.e., a substrate) and soldered to a land formed on a wall of a through-hole is known, for example, as shown in a patent document 1. In the present electronic device, a part of the insertion portion (i.e., an insertion mounting portion) of the terminal is inserted in the through-hole, and the insertion portion is connected electrically and mechanically to a land that is formed on a wall of the through-hole (i.e., a wall part of the land) by reflow soldering.
When the insertion mount structure is adopted, a contact area between the solder, the terminal and the land can be more securely reserved without increasing circuit board volume along the circuit board surface direction, in comparison to the surface mount structure. In other words, connection reliability between the solder, the terminal and the land is improved than the surface mount structure.
In addition, in the insertion mount structure, electronic parts and wiring can be arranged more closer to the through-holes on a back side of a connector mount surface of the circuit board by reflow soldering, in comparison to flow soldering. Further, when electronic parts are surface-mounted on the connector mount surface of the circuit board, the connector and the electronic parts can be simultaneously mounted on the circuit board by reflow soldering.
Some of the electronic devices have, as disclosed in a patent document 2, two kinds of connector terminals having respectively different diameters, such as a signal terminal for signal transmission and a power terminal for electric power transmission with a greater diameter than that of the signal terminal. In this case, a diameter of a through-hole in which the power terminal is inserted is greater than a diameter of a through-hole in which the signal terminal is inserted.    [Patent document 1] Japanese Patent Laid-Open No. 2009-182141 (also published as US2009/0191730)    [Patent document 2] Japanese Patent Laid-Open No. 2009-163991 (also published as US2009/0176402)
The electronic device of insertion mount structure disclosed in the patent document 2 has different through-hole diameters for different kinds of terminals. Therefore, solder 14 is filled to a deeper position of a through-hole 33 having a greater diameter than a through-hole 34 having a smaller diameter as shown in FIG. 1A, when solder paste is applied on the connector mount surface of the circuit board in a screenprinting process by reflow soldering.
Therefore, depending on an amount of filling in the through-hole, there may be a case where the solder 14 in the through-hole 33 having the greater diameter being pushed by the insertion portion of the connector (e.g., an insertion portion of a power terminal) as shown in FIG. 1B drops from a circuit board 30 out of the through-hole 33 as shown in FIG. 1C, when insertion portions 43a, 43b of the connector terminals are respectively inserted in the corresponding through-holes 33, 34.
In FIG. 1C, the illustration shows that the melted solder 14 is dropping from a through-hole at a time of reflow. In FIG. 1B, the illustration shows that the solder 14 in paste form is dropping at a time of inserting the insertion portion 43a of the terminal in the through-hole.
In contrast, dropping of the solder 14 can be restrained at a time of insertion of the insertion portion 43a of the terminal or at a time of reflow as shown in FIGS. 2B and 2C, by decreasing the amount of filling of the paste form solder 14 in the greater through-hole 33, as shown in FIG. 2A, through adjustment of printing pressure and/or printing speed of the print process.
However, because the amount of filling of the paste form solder 14 in the smaller through-hole 34 is decreased at the same time in the course of the above adjustment as shown in FIG. 2A, there may be a case where there is not a sufficient amount of the solder 14 in the through-hole 34 for providing reliability of the connection between the insertion portion 44a of the terminal and a land 36 at a time of reflow as shown in FIG. 2C.